Browser extension

Firefox

Install in Firefox — no developer mode needed. The extension is signed by Mozilla and updates itself.

Install the app first (the extension talks to it).
Open this page in Firefox 140 or newer and click Add to Firefox.
Firefox asks to allow the installation from this site: click Continue to installation, then Add.
Pin the Video Download icon (puzzle icon → pin).

Edge / Chrome

With the extension you download the video that is playing with one click, or with a right-click on a link or video. Works in Firefox, Edge and Chrome.

Installation (once)

Install the app (the extension comes with it).
In your browser open edge://extensions (Edge) or chrome://extensions (Chrome).
Turn on Developer mode and click Load unpacked.
Choose the folder %LOCALAPPDATA%\Programs\Video Download\extension. Easiest: in the app open Help → Downloading from the browser, click Copy the folder path and paste it (Ctrl+V) into the folder picker. The same window has a button that opens the extensions page in Edge or Chrome.
Pin the Video Download icon to the browser toolbar (puzzle icon → pin).

For now the extension is loaded by hand, because extension stores don't accept programs like this. The browser may therefore remind you about “Developer mode”; that is expected and the extension works normally.

Using it

Play a video on the page and click the Video Download icon: Download the playing video or Download as MP3.
Right-click a link or video: Download this link or …as MP3.
If the app isn't running, the click starts it.
Live streams and DRM-protected video are not downloaded.

After updating the app

If the extension stops responding, click Reload next to it in edge://extensions.

Mac (beta): the folder is inside the app. In the app use Help → Downloading from the browser → Copy the folder path, then in the folder picker press ⌘⇧G, paste (⌘V) and press Return.